This invention relates generally to centrifugal pumps and more particularly to multi-stage centrifugal pumps with integral disk-motors.
The practice is well established for integrating disk motors, particularly permanent-magnet, brushless DC motors, into centrifugal pumps. This is particularly focused on single-stage pumping machinery. The prior art teaches not only the configuration of the disk motor integrated with the pump but also the axial bearing and rotor position sensor configurations, double-suction design, motor cooling, and assembly/disassembly features.
Head generation and flow delivery for disk motor pumps is limited by the amount of torque which the motor, at a given diameter, can develop. The total head generated is a function of the rotor diameter and its rotation speed. The flow delivery for a given diameter and speed is determined by the impeller width. The speed of rotation is limited by both the frequency limitations of the inverter used to drive the motor and the NPSH (Net Positive Suction Head) available at the inlet of the impeller. Use of larger diameter impellers (motor disks) to develop higher pump head requires use of larger and thicker case and structural components to contain the developed head pressure as well as the higher suction pressure required.
One way to reduce the size and weight of the pump casing and components, when high heads are required, is to use small diameter impellers operating at high speeds. However, smaller diameter impellers provide smaller available disk areas to house the permanent-magnet disk motor, thereby limiting the torque that can be developed by the motor. Another limitation is the relative unavailability of motor designs (magnetic rotors and stators) that can deliver a range of pressures and flow rates.
The foregoing illustrates limitations known to exist in present centrifugal pumps driven by permanent-magnet disk motors. Thus, it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the present invention, this is accomplished by providing a two-stage, permanent-magnet, integral disk-motor centrifugal pump, comprising a housing having first and second suction ports and first and second discharge ports, said first discharge port being connected to said second suction port; a first impeller rotatably disposed on a shaft between the first suction port and the first discharge port and a second impeller placed back-to-back with said first impeller and rotatably disposed on a shaft between the second suction port and the second discharge port, each of said first and second impellers having a back shroud with an array of permanent magnets fixed thereto; a first stator and a second stator interposed between and adjacent to said first and second impellers, respectively; means for controlling rotational speed of said impellers; and means for extracting motor heat from the
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.